Hi,
try setting this parameter in /var/www/html/fog/service/ipxe/refind.conf:

# Delay for the specified number of seconds before scanning disks. # This can help some users who find that some of their disks # (usually external or optical discs) aren't detected initially, # but are detected after pressing Esc. # The default is 0. # scan_delay 5

and, if you need, this:

# Timeout in seconds for the main menu screen. Setting the timeout to 0 # disables automatic booting (i.e., no timeout). Setting it to -1 causes # an immediate boot to the default OS *UNLESS* a keypress is in the buffer # when rEFInd launches, in which case that keypress is interpreted as a # shortcut key. If no matching shortcut is found, rEFInd displays its # menu with no timeout. # timeout 5